The approach to landing and touch down on the runway of an aircraft is probably the most challenging task a pilot undertakes during normal operation. To perform the landing properly, the aircraft approaches the runway within an envelope of attitude, course, speed, and rate of descent limits. The course limits include, for example, both lateral limits and glide slope limits. An approach outside of this envelope can result in an undesirable positioning of the aircraft with respect to the runway, resulting in possibly discontinuance of the landing attempt.
In some instances visibility may be poor during approach and landing operations, resulting in what is known as instrument flight conditions. During instrument flight conditions, pilots rely on instruments, rather than visual references, to navigate the aircraft. Even during good weather conditions, pilots typically rely on instruments during the approach to some extent. Many airports and aircraft include instrument landing systems (ILS) to help guide aircraft during approach and landing operations. These systems allow for the display of a lateral deviation indicator to indicate aircraft lateral deviation from the approach course, and the display of a glide slope indicator to indicate vertical deviation from the glide slope.
Typical instrumentation of an aircraft primary flight display shows the heading by an arrow pointing on a compass and may include an aircraft symbol pointing in the direction in which the aircraft is going. The aircraft symbol may be displayed relative to a geometric symbol or set of symbols, to indicate whether the aircraft is left or right of the desired ground tract and above, below, or on the desired glide slope.
Although these known aircraft systems, including those described immediately above, are generally safe, reliable, and robust, these systems do suffer certain drawbacks. For example, if a crosswind is blowing the aircraft off of the desired ground track, the only indication to the pilot is of the aircraft symbol being displaced left or right of the desired ground track. As a result, the pilot may not readily notice the ground tract deviation and may not be timely to maneuver the aircraft (by assuming a crab angle), at least initially, to reduce course deviation due to the crosswind. In other instances, the aircraft is being flown along the desired ground track using ground based ILS but heading of the aircraft is different from this track direction due to crosswind, resulting in a crab condition. The crab angle is the difference between the heading of the aircraft and the ground track of the aircraft necessary to counteract a crosswind. Before an aircraft can be safely landed on a runway, pilot must correct the aircraft heading to align with the track direction for touch down.
Accordingly, it is desirable to provide an aircraft navigation instrumentation system and more particularly to display both the track and heading directions for performing the crosswind landing operations. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.